The present invention relates to a pneumatic tire in which the drain properties for wet-road running is improved.
Generally, when running on a wet road, the friction coefficient between the tires of an automobile and the road surface is lowered. In particular, in a case where the depth of water on the surface of a wet road is deep, or in a case where an automobile is run at a high running speed on a wet road, a layer of water is produced between the tires of the automobile and the surface of the road while running, and the friction coefficient is remarkably lowered. A state like this is called "hydroplaning". When a hydroplaning takes place, an automobile fitted with tires goes out of control, and this sometimes leads to an accident. In order to prevent the occurrence of hydroplaning like this, a tire must have good drain properties.
Conventionally, in order to improve the drain properties of a tire, a tire is adopted in which, in addition to a plurality of main grooves disposed in the circumferential direction of the tire, a plurality of sub-grooves that are bent in a V-shape in the rotational direction of the tire are also disposed in the tread surface of the tire substantially in parallel with one another with the bending points (the apexes of the V shapes) of these sub-grooves being disposed substantially centrally in the width-wise direction of the tire (the tire equator line A). However, with a so-called tread pattern having a directional property like this, the drain properties for straight running can be improved, but the tread pattern has a drawback that the drain properties at the time of turning is lowered due to the deviation of the ground-contacting center towards the width-wise direction of the tire.
In order to cope with this, a tread pattern having a directional property is proposed in which in consideration of the drain properties for turning, the bending points of sub-grooves are deviated in the width-wise direction from the equator line of the tire toward one (the outer side of the automobile) of the sides thereof. However, with a tread pattern like this, tread patterns of right tires must be different from those of left ones of an automobile, respectively, and molds of two types are required to produce tires, which is disadvantageous in the production of tires.